The present invention relates to a control valve used for a displacement variable compressor incorporated in a refrigerant circuit of an air-conditioning system for controlling the discharge displacement of the variable displacement type compressor, which can change the discharge displacement in accordance with the pressure in the crank chamber.
As shown in FIG. 10, Japanese Unexamined Patent Publication 11-324930 discloses such a control valve. This control valve mechanically detects the pressure difference between two pressure monitoring points P1 and P2, which are located in a refrigerant circuit, by a diaphragm 101. The control valve adjusts the pressure in a crank chamber by determining the position of a valve body 102 in accordance with a force that acts on the diaphragm 101 based on the pressure difference. The pressure difference reflects the flow rate of refrigerant in the refrigerant circuit. The diaphragm 101 changes the discharge displacement of the variable displacement compressor by determining the position of the valve body 102 such that the fluctuations of the pressure difference, that is, the fluctuations of the flow rate of refrigerant in the refrigerant circuit is eliminated.
The prior art control valve only has a simple internal control structure that maintains a predetermined flow rate of refrigerant. Therefore, the prior art control valve is not capable of changing the flow rate of refrigerant in the refrigerant circuit. Thus, the control valve cannot respond to the changes in the demand for air conditioning.
The objective of the present invention is to provide a control valve of a variable displacement compressor that is capable of highly accurate air-conditioning control.
To achieve the foregoing objective, the present invention also provides a control valve used for a variable displacement compressor installed in a refrigerant circuit of a vehicle air conditioner. The refrigerant circuit has a discharge pressure zone. The compressor varies the displacement in accordance with the pressure in a crank chamber. The compressor has a supply passage, which connects the crank chamber to the discharge pressure zone. The control valve comprises a valve housing. A valve chamber is defined in the valve housing to form a part of the supply passage. A valve body is accommodated in the valve chamber for adjusting the opening size of the supply passage. A pressure sensing chamber is defined in the valve housing. A pressure sensing member separates the pressure sensing chamber into a first pressure chamber and a second pressure chamber. The pressure at a first pressure monitoring point located in the refrigerant circuit is applied to the first pressure chamber. The pressure at a second pressure monitoring point located in the refrigerant circuit is applied to the second pressure chamber. The pressure sensing member moves the valve body in accordance with the pressure difference between the first pressure chamber and the second pressure chamber such that the displacement of the compressor is varied to counter changes of the pressure difference. The pressure sensing member is a bellows or a diaphragm. An actuator applies force to the pressure sensing member in accordance with external commands. The force applied by the actuator corresponds to a target value of the pressure difference. The pressure sensing member moves the valve body such that the pressure difference seeks the target value.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.